Andean Gull

Is a medium-to-large high-altitude gull that measures between 45 and 48 centimeters in length and weighs approximately 400 to 500 grams. Its breeding plumage is highly distinctive, featuring a prominent dark brown to black hood that covers the entire head, interrupted only by conspicuous white crescents behind each eye. The mantle and back of the wings are a delicate pale gray, while the rest of the body, including the neck, breast, abdomen, and tail, is a brilliant, clean white. The primary wingtips display a striking black pattern with white mirrors, which is clearly visible during flight. The bill and legs are dark red to blackish-red, and the orbital ring is a bright reddish color. Outside the breeding season, the dark hood fades almost completely, leaving only faint grayish auricular patches behind the eyes, which significantly alters its diagnostic appearance.

Geographical distribution: Is distributed continuously along the Andes mountain range, spanning territories from southern Ecuador, through the high altiplano of Peru and Bolivia, to the mountainous regions of northern Chile and northwestern Argentina. Although it is a classic inhabitant of high-altitude Andean environments, periodic altitudinal migrations are documented during the non-breeding winter season, a period in which some populations descend to lower valleys and occasionally reach the Pacific Ocean coast in Peru and northern Chile.

Habitat: Is strictly associated with high-altitude aquatic ecosystems, occurring preferentially at elevations ranging from 3,000 to 4,500 meters above sea level. Its favored habitats include high Andean lakes and lagoons, moderate-flow rivers, marshes, bofedales, peat bogs, and flooded grasslands of the puna zone. During the winter, when altiplano water bodies often freeze over, it exhibits notable ecological plasticity by migrating temporarily to coastal sandy beaches, estuaries, river mouths, and irrigated agricultural fields in the lowlands.

Feeding: Has an extremely opportunistic, versatile, and predominantly omnivorous diet. Its food intake includes a wide variety of terrestrial and aquatic invertebrates, such as earthworms, beetles, dipteran larvae, odonates, and small crustaceans captured from mud or water surfaces. It also preys on small vertebrates, including amphibians, freshwater fish, and small rodents. During the breeding season of other high-altitude waterbirds, it acts as an active predator, consuming the eggs and chicks of ducks and coots. Occasionally, it supplements its diet with carrion, human refuse, and grains in plowed agricultural fields.

Behavior: Is a highly gregarious, vocal, and remarkably bold species. It typically forms flocks of dozens of individuals to forage, roost, and migrate, though it becomes fiercely territorial and aggressive during the breeding season. Its vocalizations are loud and harsh, consisting of high-pitched, laugh-like calls used to defend territory and communicate. It is an agile and elegant flier, capable of executing rapid aerial maneuvers to catch insects on the wing or to actively mob potential predators with synchronized dive-bombing attacks.

Nesting: The breeding season of Chroicocephalus serranus peaks between November and January, coinciding with the highest availability of food resources in the high Andes. It nests either solitarily or in small, loose colonies, placing its nest on the ground on dry islets, along densely vegetated banks, or directly on floating platforms of reeds. The nest is a cup-shaped structure built from dried grasses, rushes, and feathers. The female typically lays a clutch of 2 to 3 eggs, which are greenish-brown or olive in color and heavily speckled with dark brown and gray spots. Both parents share the incubation duties for a period of approximately 24 to 26 days.

Conservation status: Is currently evaluated as Least Concern (LC) on the IUCN Red List of Threatened Species. This classification is due to its vast geographic range and a global population that is considered stable, despite lack of precise census data. Locally, however, populations face threats from the degradation of high Andean wetlands caused by mining operations, overgrazing, climate change, and excessive water extraction for agricultural and urban uses.